1. Field of the Invention
The present invention relates to a method of producing a grain oriented electrical steel sheet having a high magnetic flux and made from a thin strip casting method containing 2.5 to 4.5% by weight of Si.
2. Description of the Related Art
A grain oriented electrical steel sheet is used as an iron core material of an electrical apparatus such as a transformer etc. and thus the electrical steel sheet requires an improved excited property and watt loss as inherent magnetic properties thereof.
Further, the commercial requirements for a low watt loss material having a small energy loss have recently increased.
In the conventional production method of producing the grain oriented steel sheet, however, complex processes or treatments such as a hot rolling, cold rolling, and annealing, etc. must be used with the result that the production cost, become very expensive.
Accordingly, a technique whereby the molten electrical steel is directly worked to a thin strip by a quench solidification process has been developed, and according to this process, since a product or a semiproduct can be made from a molten steel, the production costs can be greatly reduced. There are two well known methods of producing a grain oriented electrical steel sheet by using the quench solidification process.
In the method as disclosed in Japanese Unexamined Patent Publication (Kokai) No. 59-190326, a surface energy called tertial recrystallization is used, but in this method, to generate the tertial recrystallization having {110}&lt;001&gt; orientation in the longitudinal direction, an annealing in vacuum or a high purity H.sub.2 atmosphere is required, and thus the method is not easily used in an industrial scale. Further a strip having a large thickness can not be obtained, and thus the strip obtained by the method is limited to one having a very thin thickness. In the other well known method an inhibitor is used in the same manner as in a conventional hot rolling process.
This second method, in which a hot rolling is completely omitted is disclosed, for example, Japanese Unexamined Patent Publications (Kokai) Nos. 53-97923, 54-83620, 61-238939, 63-11619, 63-176427, 64-229, etc.
In these publications, AlN, MnS, MnSe, BN, Sb etc. are proposed as inhibitors, but the inventors found that, when the hot rolling process is completely omitted and replaced by a quench solidification process, even if the secondary cooling rate, i.e., the cooling rate of the solidified strip, is made 10.degree. C./sec or more a coarse precipitate having a size of 0.1 to 1.0 .mu.m is often generated in the conventional oriented electrical molten steel compositions, and the above-mentioned inhibitors are not sufficiently reacted.